feat(providers): add Claude Fable 5 model (#5334)

Re-add claude-fable-5 (Anthropic's most capable widely released model), not marked recommended. Verified against live Anthropic API + docs:
- Pricing $10/$50 per MTok, $1 cached input (cache-read); 1M context; 128k max output; GA 2026-06-09
- Adaptive thinking only (always on, cannot be disabled) — routed via supportsAdaptiveThinking; manual budget_tokens/temperature are rejected with 400
- effort levels low/medium/high/xhigh/max (default high)
- nativeStructuredOutputs confirmed supported (live output_format json_schema call returned 200), matching same-generation siblings (Sonnet 5, Opus 4.8)

Author: waleedlatif1

apps/sim/providers/anthropic/core.ts

@@ -84,6 +84,7 @@ const THINKING_BUDGET_TOKENS: Record<string, number> = {
 
 /**
  * Checks if a model supports adaptive thinking (thinking.type: "adaptive").
+ * Fable 5 supports ONLY adaptive thinking (always on; type: "disabled" is rejected).
  * Sonnet 5 supports ONLY adaptive thinking (manual budget_tokens returns a 400 error).
  * Opus 4.8 and Opus 4.7 support ONLY adaptive thinking (no extended thinking / budget_tokens).
  * Opus 4.6 and Sonnet 4.6 support both extended and adaptive thinking — use adaptive.
@@ -92,6 +93,7 @@ const THINKING_BUDGET_TOKENS: Record<string, number> = {
 function supportsAdaptiveThinking(modelId: string): boolean {
   const normalizedModel = modelId.toLowerCase()
   return (
+    normalizedModel.includes('fable-5') ||
     normalizedModel.includes('sonnet-5') ||
     normalizedModel.includes('opus-4-8') ||
     normalizedModel.includes('opus-4.8') ||
@@ -107,7 +109,7 @@ function supportsAdaptiveThinking(modelId: string): boolean {
 /**
  * Builds the thinking configuration for the Anthropic API based on model capabilities and level.
  *
- * - Sonnet 5, Opus 4.8, Opus 4.7: Uses adaptive thinking only (no extended thinking support)
+ * - Fable 5, Sonnet 5, Opus 4.8, Opus 4.7: Uses adaptive thinking only (no extended thinking support)
  * - Opus 4.6, Sonnet 4.6: Uses adaptive thinking with effort parameter
  * - Other models: Uses budget_tokens-based extended thinking
  *

apps/sim/providers/models.ts

@@ -669,6 +669,25 @@ export const PROVIDER_DEFINITIONS: Record<string, ProviderDefinition> = {
       toolUsageControl: true,
     },
     models: [
+      {
+        id: 'claude-fable-5',
+        pricing: {
+          input: 10.0,
+          cachedInput: 1.0,
+          output: 50.0,
+          updatedAt: '2026-07-01',
+        },
+        capabilities: {
+          nativeStructuredOutputs: true,
+          maxOutputTokens: 128000,
+          thinking: {
+            levels: ['low', 'medium', 'high', 'xhigh', 'max'],
+            default: 'high',
+          },
+        },
+        contextWindow: 1000000,
+        releaseDate: '2026-06-09',
+      },
       {
         id: 'claude-sonnet-5',
         pricing: {