Improve preemptive compaction with Claude model filtering and configurable context limits

- Limit preemptive compaction to Claude models only (opus, sonnet, haiku pattern)
- Add support for detecting `anthropic-beta: context-1m-*` header to use 1M context limit for Sonnet models
- Add `getModelLimit` callback to read model limits from OpenCode config (`provider.*.models.*.limit.context`)
- Remove hardcoded MODEL_CONTEXT_LIMITS and replace with pattern-based model detection
- Cache model context limits from config at startup for performance

This enables flexible per-model context limit configuration without hardcoding limits in the plugin.

Generated with assistance of OhMyOpenCode

src/hooks/preemptive-compaction/index.ts

@@ -18,9 +18,12 @@ export interface SummarizeContext {
 
 export type BeforeSummarizeCallback = (ctx: SummarizeContext) => Promise<void> | void
 
+export type GetModelLimitCallback = (providerID: string, modelID: string) => number | undefined
+
 export interface PreemptiveCompactionOptions {
   experimental?: ExperimentalConfig
   onBeforeSummarize?: BeforeSummarizeCallback
+  getModelLimit?: GetModelLimitCallback
 }
 
 interface MessageInfo {
@@ -38,33 +41,11 @@ interface MessageWrapper {
   info: MessageInfo
 }
 
-const MODEL_CONTEXT_LIMITS: Record<string, number> = {
+const CLAUDE_MODEL_PATTERN = /claude-(opus|sonnet|haiku)/i
-  "claude-opus-4": 200_000,
+const CLAUDE_DEFAULT_CONTEXT_LIMIT = 200_000
-  "claude-sonnet-4": 200_000,
-  "claude-haiku-4": 200_000,
-  "gpt-4o": 128_000,
-  "gpt-4o-mini": 128_000,
-  "gpt-4-turbo": 128_000,
-  "gpt-4": 8_192,
-  "gpt-5": 1_000_000,
-  "o1": 200_000,
-  "o1-mini": 128_000,
-  "o1-preview": 128_000,
-  "o3": 200_000,
-  "o3-mini": 200_000,
-  "gemini-2.0-flash": 1_000_000,
-  "gemini-2.5-flash": 1_000_000,
-  "gemini-2.5-pro": 2_000_000,
-  "gemini-3-pro": 2_000_000,
-}
 
-function getContextLimit(modelID: string): number {
+function isSupportedModel(modelID: string): boolean {
-  for (const [key, limit] of Object.entries(MODEL_CONTEXT_LIMITS)) {
+  return CLAUDE_MODEL_PATTERN.test(modelID)
-    if (modelID.includes(key)) {
-      return limit
-    }
-  }
-  return 200_000
 }
 
 function createState(): PreemptiveCompactionState {
@@ -80,6 +61,7 @@ export function createPreemptiveCompactionHook(
 ) {
   const experimental = options?.experimental
   const onBeforeSummarize = options?.onBeforeSummarize
+  const getModelLimit = options?.getModelLimit
   const enabled = experimental?.preemptive_compaction !== false
   const threshold = experimental?.preemptive_compaction_threshold ?? DEFAULT_THRESHOLD
 
@@ -104,7 +86,15 @@ export function createPreemptiveCompactionHook(
     if (!tokens) return
 
     const modelID = lastAssistant.modelID ?? ""
-    const contextLimit = getContextLimit(modelID)
+    const providerID = lastAssistant.providerID ?? ""
+
+    if (!isSupportedModel(modelID)) {
+      log("[preemptive-compaction] skipping unsupported model", { modelID })
+      return
+    }
+
+    const configLimit = getModelLimit?.(providerID, modelID)
+    const contextLimit = configLimit ?? CLAUDE_DEFAULT_CONTEXT_LIMIT
     const totalUsed = tokens.input + tokens.cache.read + tokens.output
 
     if (totalUsed < MIN_TOKENS_FOR_COMPACTION) return
@@ -124,7 +114,6 @@ export function createPreemptiveCompactionHook(
     state.compactionInProgress.add(sessionID)
     state.lastCompactionTime.set(sessionID, Date.now())
 
-    const providerID = lastAssistant.providerID
     if (!providerID || !modelID) {
       state.compactionInProgress.delete(sessionID)
       return

src/index.ts

@@ -213,6 +213,20 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
   const disabledHooks = new Set(pluginConfig.disabled_hooks ?? []);
   const isHookEnabled = (hookName: HookName) => !disabledHooks.has(hookName);
 
+  const modelContextLimitsCache = new Map<string, number>();
+  let anthropicContext1MEnabled = false;
+
+  const getModelLimit = (providerID: string, modelID: string): number | undefined => {
+    const key = `${providerID}/${modelID}`;
+    const cached = modelContextLimitsCache.get(key);
+    if (cached) return cached;
+
+    if (providerID === "anthropic" && anthropicContext1MEnabled && modelID.includes("sonnet")) {
+      return 1_000_000;
+    }
+    return undefined;
+  };
+
   const todoContinuationEnforcer = isHookEnabled("todo-continuation-enforcer")
     ? createTodoContinuationEnforcer(ctx)
     : null;
@@ -261,6 +275,7 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
   const preemptiveCompaction = createPreemptiveCompactionHook(ctx, {
     experimental: pluginConfig.experimental,
     onBeforeSummarize: compactionContextInjector,
+    getModelLimit,
   });
   const rulesInjector = isHookEnabled("rules-injector")
     ? createRulesInjectorHook(ctx)
@@ -329,6 +344,31 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
     },
 
     config: async (config) => {
+      type ProviderConfig = {
+        options?: { headers?: Record<string, string> }
+        models?: Record<string, { limit?: { context?: number } }>
+      }
+      const providers = config.provider as Record<string, ProviderConfig> | undefined;
+
+      const anthropicBeta = providers?.anthropic?.options?.headers?.["anthropic-beta"];
+      anthropicContext1MEnabled = anthropicBeta?.includes("context-1m") ?? false;
+
+      if (providers) {
+        for (const [providerID, providerConfig] of Object.entries(providers)) {
+          const models = providerConfig?.models;
+          if (models) {
+            for (const [modelID, modelConfig] of Object.entries(models)) {
+              const contextLimit = modelConfig?.limit?.context;
+              if (contextLimit) {
+                modelContextLimitsCache.set(`${providerID}/${modelID}`, contextLimit);
+              }
+            }
+          }
+
+
+        }
+      }
+
       const builtinAgents = createBuiltinAgents(
         pluginConfig.disabled_agents,
         pluginConfig.agents,