proxy: implement setParamsByID filter (#535)

Add setParamsByID filter that applies different request parameters based
on the requested model ID, enabling per-alias behaviour for a single
loaded model.

- add SetParamsByID field to Filters struct and SanitizedSetParamsByID
method
- substitute ${MODEL_ID} and other macros in setParamsByID keys and
values
- validate no unknown macros remain in keys or values after substitution
- apply setParamsByID in proxyInferenceHandler after setParams (can
override it)
- update config-schema.json with setParamsByID definition
- update UI to show aliases and make them selectable in the Playground

closes #534

config-schema.json

@@ -200,11 +200,20 @@
                                 "additionalProperties": true,
                                 "default": {},
                                 "description": "Dictionary of parameters to set/override in requests. Useful for enforcing specific parameter values. Protected params like 'model' cannot be overridden. Values can be strings, numbers, booleans, arrays, or objects."
+                            },
+                            "setParamsByID": {
+                                "type": "object",
+                                "additionalProperties": {
+                                    "type": "object",
+                                    "additionalProperties": true
+                                },
+                                "default": {},
+                                "description": "Dictionary mapping requested model IDs (or aliases) to parameters to set/override in requests. Applied after setParams and can override those values. Useful with aliases to vary behaviour depending on which alias the client used (e.g. different reasoning_effort per alias). Keys support ${MODEL_ID} macro substitution. Protected params like 'model' cannot be overridden."
                             }
                         },
                         "additionalProperties": false,
                         "default": {},
-                        "description": "Dictionary of filter settings. Supports stripParams and setParams."
+                        "description": "Dictionary of filter settings. Supports stripParams, setParams, and setParamsByID."
                     },
                     "metadata": {
                         "type": "object",

config.example.yaml

@@ -126,7 +126,7 @@ apiKeys:
 # - below are examples of the all the settings a model can have
 models:
   # keys are the model names used in API requests
-  "llama":
+  "gpt-oss-120b":
     # macros: a dictionary of string substitutions specific to this model
     # - optional, default: empty dictionary
     # - macros defined here override macros defined in the global macros section
@@ -143,7 +143,7 @@ models:
     cmd: |
       # ${latest-llama} is a macro that is defined above
       ${latest-llama}
-      --model path/to/llama-8B-Q4_K_M.gguf
+      --model path/to/gpt-oss-120B.gguf
       --ctx-size ${default_ctx}
       --temperature ${temp}
 
@@ -151,13 +151,13 @@ models:
     # - optional, default: empty string
     # - if set, it will be used in the v1/models API response
     # - if not set, it will be omitted in the JSON model record
-    name: "llama 3.1 8B"
+    name: "gpt-oss 120B"
 
     # description: a description for the model
     # - optional, default: empty string
     # - if set, it will be used in the v1/models API response
     # - if not set, it will be omitted in the JSON model record
-    description: "A small but capable model used for quick testing"
+    description: "A thinking model from OpenAI"
 
     # env: define an array of environment variables to inject into cmd's environment
     # - optional, default: empty array
@@ -172,14 +172,6 @@ models:
     # - if you use a custom port in cmd this *must* be set
     proxy: http://127.0.0.1:8999
 
-    # aliases: alternative model names that this model configuration is used for
-    # - optional, default: empty array
-    # - aliases must be unique globally
-    # - useful for impersonating a specific model
-    aliases:
-      - "gpt-4o-mini"
-      - "gpt-3.5-turbo"
-
     # checkEndpoint: URL path to check if the server is ready
     # - optional, default: /health
     # - endpoint is expected to return an HTTP 200 response
@@ -197,7 +189,7 @@ models:
     # - optional, default: ""
     # - useful for when the upstream server expects a specific model name that
     #   is different from the model's ID
-    useModelName: "qwen:qwq"
+    useModelName: "openai/gpt-oss-120B"
 
     # filters: a dictionary of filter settings
     # - optional, default: empty dictionary
@@ -216,11 +208,38 @@ models:
       # - useful for enforcing specific parameter values
       # - protected params like "model" cannot be overridden
       # - values can be strings, numbers, booleans, arrays, or objects
+      # - always runs for the model
       setParams:
         # Example: enforce specific sampling parameters
         temperature: 0.7
         top_p: 0.9
 
+      # setParamsByID: a dictionary of parameters to set based the model ID
+      # - optional, default: empty dictionary
+      # - combine with aliases to create variant behaviour without reloading the model
+      # - parameters are set in the request body JSON
+      # - run after setParams so it will override any settings
+      # - protected params like "model" cannot be overridden
+      # - values can be strings, numbers, booleans, arrays, or objects
+      # - model aliases will be automatically created for each key
+      setParamsByID:
+        "${MODEL_ID}":
+          chat_template_kwargs:
+            reasoning_effort: medium
+        "${MODEL_ID}:high":
+          chat_template_kwargs:
+            reasoning_effort: high
+        "${MODEL_ID}:low":
+          chat_template_kwargs:
+            reasoning_effort: low
+
+    # aliases: alternative model names that this model configuration is used for
+    # - optional, default: empty array
+    # - aliases must be unique globally
+    # - useful for impersonating a specific model
+    aliases:
+      - "gpt-4o-mini"
+
     # metadata: a dictionary of arbitrary values that are included in /v1/models
     # - optional, default: empty dictionary
     # - while metadata can contains complex types it is recommended to keep it simple

proxy/config/config.go

@@ -294,6 +294,24 @@ func LoadConfigFromReader(r io.Reader) (Config, error) {
 			modelConfig.CheckEndpoint = strings.ReplaceAll(modelConfig.CheckEndpoint, macroSlug, macroStr)
 			modelConfig.Filters.StripParams = strings.ReplaceAll(modelConfig.Filters.StripParams, macroSlug, macroStr)
 
+			// Substitute macros in SetParamsByID keys and values
+			if len(modelConfig.Filters.SetParamsByID) > 0 {
+				newSetParamsByID := make(map[string]map[string]any, len(modelConfig.Filters.SetParamsByID))
+				for key, paramMap := range modelConfig.Filters.SetParamsByID {
+					newKey := strings.ReplaceAll(key, macroSlug, macroStr)
+					newValAny, err := substituteMacroInValue(any(paramMap), entry.Name, entry.Value)
+					if err != nil {
+						return Config{}, fmt.Errorf("model %s filters.setParamsByID: %s", modelId, err.Error())
+					}
+					newParamMap, ok := newValAny.(map[string]any)
+					if !ok {
+						return Config{}, fmt.Errorf("model %s filters.setParamsByID: unexpected type after macro substitution", modelId)
+					}
+					newSetParamsByID[newKey] = newParamMap
+				}
+				modelConfig.Filters.SetParamsByID = newSetParamsByID
+			}
+
 			// Substitute in metadata (type-preserving)
 			if len(modelConfig.Metadata) > 0 {
 				result, err := substituteMacroInValue(modelConfig.Metadata, entry.Name, entry.Value)
@@ -359,6 +377,34 @@ func LoadConfigFromReader(r io.Reader) (Config, error) {
 			}
 		}
 
+		// Validate SetParamsByID keys and values
+		for key, paramMap := range modelConfig.Filters.SetParamsByID {
+			if matches := macroPatternRegex.FindAllStringSubmatch(key, -1); len(matches) > 0 {
+				return Config{}, fmt.Errorf("unknown macro '${%s}' found in model %s filters.setParamsByID key", matches[0][1], modelId)
+			}
+			if err := validateNestedForUnknownMacros(any(paramMap), fmt.Sprintf("model %s filters.setParamsByID[%s]", modelId, key)); err != nil {
+				return Config{}, err
+			}
+		}
+
+		// Auto-register setParamsByID keys as aliases (skip the model's own ID)
+		for key := range modelConfig.Filters.SetParamsByID {
+			if key == modelId {
+				continue
+			}
+			if _, exists := config.Models[key]; exists {
+				return Config{}, fmt.Errorf("model %s filters.setParamsByID: key '%s' conflicts with an existing model ID", modelId, key)
+			}
+			if existingModel, exists := config.aliases[key]; exists {
+				if existingModel != modelId {
+					return Config{}, fmt.Errorf("duplicate alias '%s' in model %s filters.setParamsByID, already used by model %s", key, modelId, existingModel)
+				}
+				continue // already registered as explicit alias for this model
+			}
+			config.aliases[key] = modelId
+			modelConfig.Aliases = append(modelConfig.Aliases, key)
+		}
+
 		if _, err := url.Parse(modelConfig.Proxy); err != nil {
 			return Config{}, fmt.Errorf("model %s: invalid proxy URL: %w", modelId, err)
 		}

proxy/config/filters.go

@@ -20,6 +20,12 @@ type Filters struct {
 	// SetParams is a dictionary of parameters to set/override in requests
 	// Protected params (like "model") cannot be set
 	SetParams map[string]any `yaml:"setParams"`
+
+	// SetParamsByID maps requested model IDs to parameters to set/override in requests.
+	// Useful with aliases: a single loaded model can behave differently depending on
+	// which alias the client used. Applied after SetParams, so it can override those values.
+	// Protected params (like "model") cannot be set.
+	SetParamsByID map[string]map[string]any `yaml:"setParamsByID"`
 }
 
 // SanitizedStripParams returns a sorted list of parameters to strip,
@@ -51,6 +57,33 @@ func (f Filters) SanitizedStripParams() []string {
 	return cleaned
 }
 
+// SanitizedSetParamsByID returns the params to set for the given requestedModelID,
+// with protected params removed and keys sorted for consistent iteration order.
+// Returns nil if the ID has no entry or all its params are protected.
+func (f Filters) SanitizedSetParamsByID(requestedModelID string) (map[string]any, []string) {
+	if len(f.SetParamsByID) == 0 {
+		return nil, nil
+	}
+	params, found := f.SetParamsByID[requestedModelID]
+	if !found || len(params) == 0 {
+		return nil, nil
+	}
+	result := make(map[string]any, len(params))
+	keys := make([]string, 0, len(params))
+	for key, value := range params {
+		if slices.Contains(ProtectedParams, key) {
+			continue
+		}
+		result[key] = value
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	if len(result) == 0 {
+		return nil, nil
+	}
+	return result, keys
+}
+
 // SanitizedSetParams returns a copy of SetParams with protected params removed
 // and keys sorted for consistent iteration order
 func (f Filters) SanitizedSetParams() (map[string]any, []string) {

proxy/config/filters_test.go

@@ -162,6 +162,123 @@ func TestFilters_SanitizedSetParams(t *testing.T) {
 	}
 }
 
+func TestFilters_SanitizedSetParamsByID(t *testing.T) {
+	tests := []struct {
+		name             string
+		setParamsByID    map[string]map[string]any
+		requestedModelID string
+		wantParams       map[string]any
+		wantKeys         []string
+	}{
+		{
+			name:             "empty SetParamsByID returns nil",
+			setParamsByID:    nil,
+			requestedModelID: "model1",
+			wantParams:       nil,
+			wantKeys:         nil,
+		},
+		{
+			name:             "empty map returns nil",
+			setParamsByID:    map[string]map[string]any{},
+			requestedModelID: "model1",
+			wantParams:       nil,
+			wantKeys:         nil,
+		},
+		{
+			name: "non-matching model ID returns nil",
+			setParamsByID: map[string]map[string]any{
+				"model2": {"temperature": 0.9},
+			},
+			requestedModelID: "model1",
+			wantParams:       nil,
+			wantKeys:         nil,
+		},
+		{
+			name: "matching model ID returns correct params",
+			setParamsByID: map[string]map[string]any{
+				"model1": {"temperature": 0.7, "top_p": 0.9},
+				"model2": {"temperature": 0.5},
+			},
+			requestedModelID: "model1",
+			wantParams: map[string]any{
+				"temperature": 0.7,
+				"top_p":       0.9,
+			},
+			wantKeys: []string{"temperature", "top_p"},
+		},
+		{
+			name: "protected param model is filtered out",
+			setParamsByID: map[string]map[string]any{
+				"model1": {
+					"model":       "should-be-filtered",
+					"temperature": 0.7,
+				},
+			},
+			requestedModelID: "model1",
+			wantParams: map[string]any{
+				"temperature": 0.7,
+			},
+			wantKeys: []string{"temperature"},
+		},
+		{
+			name: "only protected param returns nil",
+			setParamsByID: map[string]map[string]any{
+				"model1": {
+					"model": "should-be-filtered",
+				},
+			},
+			requestedModelID: "model1",
+			wantParams:       nil,
+			wantKeys:         nil,
+		},
+		{
+			name: "keys are sorted",
+			setParamsByID: map[string]map[string]any{
+				"model1": {
+					"z_param": "z",
+					"a_param": "a",
+					"m_param": "m",
+				},
+			},
+			requestedModelID: "model1",
+			wantParams: map[string]any{
+				"z_param": "z",
+				"a_param": "a",
+				"m_param": "m",
+			},
+			wantKeys: []string{"a_param", "m_param", "z_param"},
+		},
+		{
+			name: "alias style key lookup",
+			setParamsByID: map[string]map[string]any{
+				"model1:high": {"reasoning_effort": "high"},
+				"model1:low":  {"reasoning_effort": "low"},
+			},
+			requestedModelID: "model1:high",
+			wantParams: map[string]any{
+				"reasoning_effort": "high",
+			},
+			wantKeys: []string{"reasoning_effort"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			f := Filters{SetParamsByID: tt.setParamsByID}
+			gotParams, gotKeys := f.SanitizedSetParamsByID(tt.requestedModelID)
+
+			if tt.wantParams == nil {
+				assert.Nil(t, gotParams)
+				assert.Nil(t, gotKeys)
+				return
+			}
+
+			assert.Equal(t, tt.wantKeys, gotKeys)
+			assert.Equal(t, tt.wantParams, gotParams)
+		})
+	}
+}
+
 func TestProtectedParams(t *testing.T) {
 	// Verify that "model" is protected
 	assert.Contains(t, ProtectedParams, "model")

proxy/config/model_config_test.go

@@ -73,6 +73,72 @@ models:
 	}
 }
 
+func TestConfig_SetParamsByIDAutoAlias(t *testing.T) {
+	content := `
+models:
+  model1:
+    cmd: path/to/cmd --port ${PORT}
+    filters:
+      setParamsByID:
+        "${MODEL_ID}:high":
+          reasoning_effort: high
+        "${MODEL_ID}:low":
+          reasoning_effort: low
+`
+	cfg, err := LoadConfigFromReader(strings.NewReader(content))
+	assert.NoError(t, err)
+
+	// Keys (other than the model's own ID) should be registered as aliases
+	realName, found := cfg.RealModelName("model1:high")
+	assert.True(t, found, "model1:high should be an auto-registered alias")
+	assert.Equal(t, "model1", realName)
+
+	realName, found = cfg.RealModelName("model1:low")
+	assert.True(t, found, "model1:low should be an auto-registered alias")
+	assert.Equal(t, "model1", realName)
+
+	// Auto-aliases should also appear in modelConfig.Aliases
+	aliases := cfg.Models["model1"].Aliases
+	assert.Contains(t, aliases, "model1:high")
+	assert.Contains(t, aliases, "model1:low")
+}
+
+func TestConfig_SetParamsByIDAutoAliasConflictWithModelID(t *testing.T) {
+	content := `
+models:
+  model1:
+    cmd: path/to/cmd --port ${PORT}
+    filters:
+      setParamsByID:
+        model2:
+          reasoning_effort: high
+  model2:
+    cmd: path/to/cmd --port ${PORT}
+`
+	_, err := LoadConfigFromReader(strings.NewReader(content))
+	assert.ErrorContains(t, err, "conflicts with an existing model ID")
+}
+
+func TestConfig_SetParamsByIDAutoAliasConflictWithOtherModel(t *testing.T) {
+	content := `
+models:
+  model1:
+    cmd: path/to/cmd --port ${PORT}
+    filters:
+      setParamsByID:
+        "shared-alias":
+          reasoning_effort: high
+  model2:
+    cmd: path/to/cmd --port ${PORT}
+    filters:
+      setParamsByID:
+        "shared-alias":
+          reasoning_effort: low
+`
+	_, err := LoadConfigFromReader(strings.NewReader(content))
+	assert.ErrorContains(t, err, "duplicate alias")
+}
+
 func TestConfig_ModelFiltersWithSetParams(t *testing.T) {
 	content := `
 models:

proxy/proxymanager.go

@@ -720,6 +720,17 @@ func (pm *ProxyManager) proxyInferenceHandler(c *gin.Context) {
 			}
 		}
 
+		// setParamsByID: set params based on the requested model ID (runs after setParams, can override it)
+		setParamsByIDParams, setParamsByIDKeys := pm.config.Models[modelID].Filters.SanitizedSetParamsByID(requestedModel)
+		for _, key := range setParamsByIDKeys {
+			pm.proxyLogger.Debugf("<%s> setting param by id: %s", requestedModel, key)
+			bodyBytes, err = sjson.SetBytes(bodyBytes, key, setParamsByIDParams[key])
+			if err != nil {
+				pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error setting parameter %s in request", key))
+				return
+			}
+		}
+
 		pm.proxyLogger.Debugf("ProxyManager using local Process for model: %s", requestedModel)
 		nextHandler = processGroup.ProxyRequest
 	} else if pm.peerProxy != nil && pm.peerProxy.HasPeerModel(requestedModel) {

proxy/proxymanager_api.go

@@ -14,12 +14,13 @@ import (
 )
 
 type Model struct {
-	Id          string `json:"id"`
-	Name        string `json:"name"`
-	Description string `json:"description"`
-	State       string `json:"state"`
-	Unlisted    bool   `json:"unlisted"`
-	PeerID      string `json:"peerID"`
+	Id          string   `json:"id"`
+	Name        string   `json:"name"`
+	Description string   `json:"description"`
+	State       string   `json:"state"`
+	Unlisted    bool     `json:"unlisted"`
+	PeerID      string   `json:"peerID"`
+	Aliases     []string `json:"aliases,omitempty"`
 }
 
 func addApiHandlers(pm *ProxyManager) {
@@ -83,6 +84,7 @@ func (pm *ProxyManager) getModelStatus() []Model {
 			Description: pm.config.Models[modelID].Description,
 			State:       state,
 			Unlisted:    pm.config.Models[modelID].Unlisted,
+			Aliases:     pm.config.Models[modelID].Aliases,
 		})
 	}
 

proxy/proxymanager_test.go

@@ -1046,6 +1046,61 @@ func TestProxyManager_FiltersStripParams(t *testing.T) {
 	// t.Logf("%v", response)
 }
 
+func TestProxyManager_FiltersSetParamsByID(t *testing.T) {
+	// no explicit aliases — setParamsByID keys are auto-registered as aliases
+	configStr := strings.Replace(`
+logLevel: error
+models:
+  model1:
+    cmd: 'SRPATH --port ${PORT} --silent --respond model1'
+    proxy: "http://127.0.0.1:${PORT}"
+    filters:
+      setParams:
+        reasoning_effort: medium
+      setParamsByID:
+        "${MODEL_ID}:high":
+          reasoning_effort: high
+        "${MODEL_ID}:low":
+          reasoning_effort: low
+`, "SRPATH", simpleResponderPath, -1)
+
+	cfg, err := config.LoadConfigFromReader(strings.NewReader(configStr))
+	if !assert.NoError(t, err, "invalid test configuration") {
+		return
+	}
+
+	proxy := New(cfg)
+	defer proxy.StopProcesses(StopWaitForInflightRequest)
+
+	tests := []struct {
+		requestedModel string
+		wantEffort     string
+	}{
+		// setParams applies, no setParamsByID match
+		{requestedModel: "model1", wantEffort: "medium"},
+		// setParamsByID overrides setParams
+		{requestedModel: "model1:high", wantEffort: "high"},
+		{requestedModel: "model1:low", wantEffort: "low"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.requestedModel, func(t *testing.T) {
+			reqBody := fmt.Sprintf(`{"model":%q}`, tt.requestedModel)
+			req := httptest.NewRequest("POST", "/v1/chat/completions", bytes.NewBufferString(reqBody))
+			w := CreateTestResponseRecorder()
+			proxy.ServeHTTP(w, req)
+			assert.Equal(t, http.StatusOK, w.Code)
+
+			var response map[string]interface{}
+			assert.NoError(t, json.Unmarshal(w.Body.Bytes(), &response))
+
+			requestBody, _ := response["request_body"].(string)
+			gotEffort := gjson.Get(requestBody, "reasoning_effort").String()
+			assert.Equal(t, tt.wantEffort, gotEffort, "reasoning_effort mismatch for model %s", tt.requestedModel)
+		})
+	}
+}
+
 func TestProxyManager_HealthEndpoint(t *testing.T) {
 	config := config.AddDefaultGroupToConfig(config.Config{
 		HealthCheckTimeout: 15,

ui-svelte/src/components/LogPanel.svelte

@@ -65,10 +65,17 @@
   });
 
   let preElement: HTMLPreElement;
+  let userScrolledUp = $state(false);
 
-  // Auto scroll to bottom when logs change
+  function handleScroll() {
+    if (!preElement) return;
+    const { scrollTop, scrollHeight, clientHeight } = preElement;
+    userScrolledUp = scrollHeight - scrollTop - clientHeight > 40;
+  }
+
+  // Auto scroll to bottom when logs change, unless user has scrolled up
   $effect(() => {
-    if (preElement && filteredLogs) {
+    if (preElement && filteredLogs && !userScrolledUp) {
       preElement.scrollTop = preElement.scrollHeight;
     }
   });
@@ -127,6 +134,6 @@
     {/if}
   </div>
   <div class="rounded-lg bg-background font-mono text-sm flex-1 overflow-hidden">
-    <pre bind:this={preElement} class="{textWrapClass} {fontSizeClass} h-full overflow-auto p-4">{filteredLogs}</pre>
+    <pre bind:this={preElement} onscroll={handleScroll} class="{textWrapClass} {fontSizeClass} h-full overflow-auto p-4">{filteredLogs}</pre>
   </div>
 </div>

ui-svelte/src/components/ModelsPanel.svelte

@@ -165,6 +165,9 @@
               {#if model.description}
                 <p class={model.unlisted ? "text-opacity-70" : ""}><em>{model.description}</em></p>
               {/if}
+              {#if model.aliases && model.aliases.length > 0}
+                <p class="text-xs text-txtsecondary">Aliases: {model.aliases.join(", ")}</p>
+              {/if}
             </td>
             <td class="w-12">
               {#if model.state === "stopped"}

ui-svelte/src/components/playground/ModelSelector.svelte

@@ -25,6 +25,11 @@
       <optgroup label="Local">
         {#each grouped.local as model (model.id)}
           <option value={model.id}>{model.id}</option>
+          {#if model.aliases}
+            {#each model.aliases as alias (alias)}
+              <option value={alias}>  ↳ {alias}</option>
+            {/each}
+          {/if}
         {/each}
       </optgroup>
     {/if}

ui-svelte/src/lib/types.ts

@@ -9,6 +9,7 @@ export interface Model {
   description: string;
   unlisted: boolean;
   peerID: string;
+  aliases?: string[];
 }
 
 export interface Metrics {