Model comparison

Claude Haiku 4.5 vs Claude Mythos 5.1

Two Anthropic tiers compared on the figures that decide which one a workload actually needs.

Catalog record checked September 5, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Haiku 4.5

Budget

Anthropic

Claude Mythos 5.1

Frontier

AI model capability comparison
Specification	Claude Haiku 4.5	Claude Mythos 5.1
Provider	Anthropic	Anthropic
Tier	Budget	Frontier
Context window	200K	Not verifiedUnverified
Max output	64K	Not verifiedUnverified
Input / 1M tokens	Winner: $1	$10
Output / 1M tokens	Winner: $5	$50
Weights	Closed	Closed
Parameters	Not disclosedUnverified	cyber/bio research variant of Fable 5.1
Reasoning levels	Not verifiedUnverified	adaptive
Modalities	text, image	text, image
API model id	claude-haiku-4-5-20251001	claude-mythos-5
Released	October 15, 2025	September 1, 2026
Artificial Analysis Intelligence Index (2026-08-14)	28	Not verifiedUnverified
SWE-bench Verified (2026-02-17)	66.6	Not verifiedUnverified
Terminal-Bench (2025-10-15)	40.21	Not verifiedUnverified

Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

2026-08-14: Artificial Analysis (Non-reasoning)Composite index blending reasoning, knowledge, and coding evals into one 0–100 score. Comparability: directly comparable — AA occasionally rebaselines the index scale between snapshots — a score captured on one date is only comparable to same-snapshot scores (check measuredAt).
2026-02-17: SWE-bench official leaderboard (independent harness: mini-SWE-agent bash-only, $0.33/task; conflicts with vendor 73.3 — both preserved)Real GitHub issue resolution: does the model's patch pass the hidden tests. Comparability: comparable with caveat — Post-audit vendor claims and pre-audit scores sit on different task trust levels; scaffolding (agent harness, compute budget) also dominates results. Never aggregate across scaffolds.
2025-10-15: Anthropic — Introducing Claude Haiku 4.5 (vendor, Terminus 2, no thinking, 6 runs; 41.75 with 32K thinking)Real GitHub issue resolution: does the model's patch pass the hidden tests. Comparability: comparable with caveat — Post-audit vendor claims and pre-audit scores sit on different task trust levels; scaffolding (agent harness, compute budget) also dominates results. Never aggregate across scaffolds.

Pricing tiers: Claude Haiku 4.5: Standard $1/$5 per MTok; cache reads 10% of base input. 200K context (vs 1M on Opus/Sonnet 5). · Claude Mythos 5.1: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview.

BudgetRecord checked September 5, 2026

Claude Haiku 4.5

Claude Haiku 4.5 is Anthropic's fastest, cheapest tier for high-volume classification and extraction.

Best for

High-volume classification
Routine extraction
Latency-sensitive stacks

Watch out

No adaptive thinking; 200K context only. A generation behind Opus/Sonnet 5 — Anthropic lists 2026-10-15 as the earliest possible retirement date.

FrontierRecord checked September 3, 2026

Claude Mythos 5.1

Claude Mythos 5.1 is Anthropic's most capable model for cybersecurity and biology research — the Fable 5.1 model with fewer cyber/bio safeguards, restricted to vetted US organisations.

Best for

Cyber-defence research
Biology research
Claude Security workloads

Watch out

Invite-only (vetted US organisations, verification programmes); 30-day data retention applies by default. Same underlying model as Fable 5.1 — most teams should just use Fable.

When the cheaper one wins

Claude Haiku 4.5 is cheaper on output at $5 per million tokens against $50 for Claude Mythos 5.1 — about 10×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.

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Evidence confidence: Medium

How strong and complete the evidence behind this comparison is — not a prediction of which model is better.

Pricing verified on both sides — Input and output rates are verified for both models.
1/5 core specs verified on both sides — Not published for at least one side: context window, max output, parameter count, reasoning levels.
No shared named benchmark — No benchmark has been measured on both models.
Verified within the last 90 days — Newest catalog check was 6 days ago.
Both models carry source citations — Each side has at least two catalog sources on record.

Source receipts

Each catalog figure was checked against the provider or an independent second source on the date shown.

Claude Haiku 4.5: Anthropic — Claude Haiku 4.5 (accessed 2026-08-29)
Claude Haiku 4.5: Anthropic pricing (accessed 2026-08-29)
Claude Mythos 5.1: Anthropic — Claude Mythos (accessed 2026-09-03)
Claude Mythos 5.1: Anthropic — model deprecations (claude-mythos-5) (accessed 2026-09-03)

Related comparisons

Diving deeper on one model? Claude Haiku 4.5 · Claude Mythos 5.1

Common questions

Claude Haiku 4.5 vs Claude Mythos 5.1

Answered from the verified figures on this page rather than general guidance.

Is Claude Haiku 4.5 or Claude Mythos 5.1 cheaper for input?

Claude Haiku 4.5 is cheaper at $1 per million input tokens, against $10 for Claude Mythos 5.1 — roughly 10× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Haiku 4.5 has tiered pricing: Standard $1/$5 per MTok; cache reads 10% of base input. 200K context (vs 1M on Opus/Sonnet 5). Claude Mythos 5.1 has tiered pricing: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview.

Is Claude Haiku 4.5 or Claude Mythos 5.1 cheaper for output?

Claude Haiku 4.5 is cheaper at $5 per million output tokens, against $50 for Claude Mythos 5.1 — roughly 10× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Haiku 4.5 has tiered pricing: Standard $1/$5 per MTok; cache reads 10% of base input. 200K context (vs 1M on Opus/Sonnet 5). Claude Mythos 5.1 has tiered pricing: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview.

Should I use Claude Haiku 4.5 or Claude Mythos 5.1?

Claude Haiku 4.5 is the budget tier and Claude Mythos 5.1 the frontier tier. The useful question is whether your hardest task actually fails on the cheaper one — most production volume such as classification, extraction and summarisation does not.

Next step

Choosing between them

The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.

Input price: Claude Haiku 4.5 costs $1 per 1M tokens versus $10 for Claude Mythos 5.1 — a 10x difference at the headline tier.
Positioning: Claude Haiku 4.5 sits in the budget tier, Claude Mythos 5.1 in the frontier tier — most production volume (classification, extraction, summarisation) does not need the pricier tier.

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