Claude Fable 5 vs Grok 4.5
Grok 4.5 and Claude Fable 5 are the strongest current xAI-versus-Anthropic frontier comparison for builders evaluating coding agents, long-context API work, and enterprise workflow automation. Grok 4.5 launched July 8, 2026 with tiered xAI API pricing and Grok Build distribution. Claude Fable 5 is Anthropic's generally released Mythos-class model with adaptive thinking, refusal handling, and a documented June launch, June suspension, and July redeploy timeline.
Pick Grok 4.5 when lower standard-tier API economics ($2/$6 per 1M tokens up to 200K prompt tokens), Grok Build or Cursor distribution, and xAI-first coding launch claims matter most, while accepting first-party-only chart rows for some benchmarks. Pick Claude Fable 5 when Anthropic's stronger sourced agentic coding evidence and adaptive thinking fit the workload and you have verified live Fable 5 access, accepting higher $10/$50 launch pricing and explicit safety-classifier behavior. This is the flagship xAI-versus-Anthropic route; use Sonnet 5 only for balanced-tier product comparisons.
Decision scorecard
Local evidence first| Signal | Claude Fable 5 | Grok 4.5 |
|---|---|---|
| Product type | Standalone API model | Coding-specialized model |
| Best for | reasoning-heavy apps, multimodal apps, and tool-calling agents | custom coding agents, code generation, and tool loops |
| Decision fit | Coding, RAG, and Agents | Coding, RAG, and Agents |
| Context window | 1m | 500k |
| Cheapest output | $50/1M tokens | $6/1M tokens |
| Provider routes | 8 tracked | 3 tracked |
| Shared benchmarks | SWE-bench Pro leader | 1 shared |
Decision tradeoffs
- Claude Fable 5 holds a shared-benchmark lead on SWE-bench Pro, ahead by 15.6 points.
- Claude Fable 5 has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Claude Fable 5 has broader tracked provider coverage for fallback and procurement flexibility.
- Claude Fable 5 uniquely exposes Structured outputs in local model data.
- Local decision data tags Claude Fable 5 for Coding, RAG, and Agents.
- Grok 4.5 has the lower cheapest tracked output price at $6/1M tokens.
- Grok 4.5 uniquely exposes Code execution in local model data.
- Local decision data tags Grok 4.5 for Coding, RAG, and Agents.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Claude Fable 5
$20,500
Cheapest tracked route/tier: Anthropic
Grok 4.5
$3,100
Cheapest tracked route/tier: xAI Console <=200K prompt tokens
Estimated monthly gap: $17,400. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- Provider overlap exists on OpenRouter and Vercel AI Gateway; start route-level A/B tests there.
- Grok 4.5 is $44/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Structured outputs before moving production traffic.
- Grok 4.5 adds Code execution in local capability data.
- Provider overlap exists on OpenRouter and Vercel AI Gateway; start route-level A/B tests there.
- Claude Fable 5 is $44/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Code execution before moving production traffic.
- Claude Fable 5 adds Structured outputs in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-06-09 | 2026-07-08 |
| Context window | 1m | 500k |
| Parameters | — | — |
| Architecture | Decoder Only | - |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Weights | Not released | Not released |
| Code | Unknown | Unknown |
| Commercial use | Commercial use: conditional | Commercial use: conditional |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | Claude Fable 5 | Grok 4.5 |
|---|---|---|
| Input price | $10/1M tokens |
|
| Output price | $50/1M tokens |
|
| Providers |
Capabilities
| Capability | Claude Fable 5 | Grok 4.5 |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | Yes | Yes |
| Function calling | Yes | Yes |
| Tool use | Yes | Yes |
| Structured outputs | Yes | No |
| Code execution | No | Yes |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
| Benchmark | Claude Fable 5 | Grok 4.5 |
|---|---|---|
| SWE-bench Pro | 80.3 | 64.7 |
Deep dive
Pricing strongly favors Grok 4.5 on the tracked standard tier. xAI lists Grok 4.5 at $2/M input and $6/M output for prompts up to 200K tokens, with a higher tier above 200K. Anthropic's tracked Fable 5 launch pricing is $10/M input and $50/M output with a 1M-token context window and up to 128K output tokens.
Anthropic product behavior is a first-class differentiator. Claude Fable 5 includes safety classifiers and refusal handling that can affect biology, cybersecurity, and distillation prompts, and some requests may route differently than a plain Opus call. Grok 4.5 has its own EU launch-day availability caveat rather than Anthropic-style refusal routing, so integration testing should cover both access and policy behavior.
Benchmark evidence is asymmetric and source-labeled. Fable 5 has seeded rows such as SWE-bench Pro 80.3%, Vals.ai SWE-bench Verified 96%, OSWorld-Verified 85.0%, and GDPval-AA ELO 1932. Grok 4.5 has xAI chart rows for Terminal Bench 2.1, SWE Bench Pro, and DeepSWE variants plus a shared DeepSWE 1.1 row at 53%. Do not treat xAI chart-only values as independently verified without naming the evaluator.
Availability timelines differ. Grok 4.5 is tracked as available through xAI API/console routes with an EU launch-day limitation. Claude Fable 5 launched June 9, was suspended June 12, and Anthropic says it redeployed July 1; verify live access on Claude API or cloud partner routes before production.
For procurement, treat this as a live test pair. Token price, refusal behavior, provider region coverage, and your own coding-agent harness usually matter more than any single launch-chart delta once both models are callable on your stack.
FAQ
Which is cheaper to run through the API?
Grok 4.5 is cheaper on the tracked standard tier at $2/M input and $6/M output for prompts up to 200K tokens. Claude Fable 5 launch pricing is $10/M input and $50/M output. Compare your real prompt length because Grok adds a higher tier above 200K tokens and Fable 5 batch pricing may change effective cost.
How do Grok 4.5 and Claude Fable 5 handle high-risk or refused requests?
Claude Fable 5 documents safety classifiers and refusal behavior that can affect some high-risk topics and integration paths. Grok 4.5 does not share that exact Anthropic policy model, but xAI's launch notes EU availability limits that can block some deployments. Test both access and policy behavior on your provider route.
Which model has stronger independently sourced benchmark evidence?
Claude Fable 5 has stronger mix of Anthropic launch and independent rows such as Vals.ai SWE-bench Verified in the seed. Grok 4.5 has useful DeepSWE and chart rows, but several July 2026 xAI chart values are first-party only and should be labeled directional until harness documentation or independent leaderboard confirmation arrives.
Should I compare Grok 4.5 with Claude Sonnet 5 instead?
Use Grok 4.5 versus Claude Fable 5 for flagship-to-flagship claims. Sonnet 5 is useful for balanced-tier product selection, but Fable 5 is the stronger sourced Anthropic comparator for July 2026 frontier intent.
Continue comparing
Last reviewed: 2026-07-09. Data sourced from public model cards and provider documentation.