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.

Recorded profile verification October 1, 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
Provider	Anthropic	Anthropic
Tier
Tier	Budget	Frontier
Context window
Context window	200K	Winner: 1M
Max output
Max output	64K	Winner: 128K
Input / 1M tokens
Input / 1M tokens	Winner: $1	$10
Output / 1M tokens
Output / 1M tokens	Winner: $5	$50
Weights
Weights	Closed	Closed
Parameters
Parameters	Not verifiedUnverified	Not verifiedUnverified
Reasoning levels
Reasoning levels	extended thinking (budget_tokens)	low, medium, high, xhigh, max
Modalities
Modalities	text, image	text, image
API model id
API model id	claude-haiku-4-5-20251001	claude-mythos-5-1
Released
Released	October 15, 2025	September 1, 2026
SWE-bench Verified [high] · source date Claude Haiku 4.5: 2026-02-17
SWE-bench Verified [high] · source date Claude Haiku 4.5: 2026-02-17	66.6	Not verifiedUnverified
SWE-bench Verified · source date Claude Haiku 4.5: 2025-10-15
SWE-bench Verified · source date Claude Haiku 4.5: 2025-10-15	73.3	Not verifiedUnverified
Terminal-Bench · source date Claude Haiku 4.5: 2025-10-15
Terminal-Bench · source date Claude Haiku 4.5: 2025-10-15	40.21	Not verifiedUnverified

Dates beside benchmark scores refer to the linked source’s publication or capture date unless that source explicitly states when it measured the result. A shared URL alone does not establish comparable runs; unverified setups are marked. Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

Where each score comes from, and how far it can be compared across models.

Source date2026-02-17
SWE-bench official submission metadata (66.6%, $0.330924/task; distinct from Anthropic vendor 73.3%) (mini-SWE-agent 2.0.0; bash-only, single attempt; published submission February17,2026)
Real GitHub issue resolution: does the model's patch pass the hidden tests.
Comparable with caveatPost-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.
Source date2025-10-15
Anthropic — Introducing Claude Haiku 4.5 (vendor, Terminus 2, no thinking, 6 runs; 41.75 with 32K thinking)
Source date2025-10-15
Anthropic — Introducing Claude Haiku 4.5 (vendor, avg of 50 trials, 128K thinking budget)
Real GitHub issue resolution: does the model's patch pass the hidden tests.
Comparable with caveatPost-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 $0.10, 5-minute writes $1.25 and 1-hour writes $2. Batch $0.50/$2.50. Context 200K and output 64K. Reliable knowledge cutoff Feb 2025; training cutoff Jul 2025. The alias claude-haiku-4-5 resolves to claude-haiku-4-5-20251001. Retirement not sooner than October 15, 2026; no definite shutdown is announced.

Claude Mythos 5.1: Standard $10/$50 per MTok, sharing Fable 5.1's specifications/pricing. Cache reads $0.25; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Invite-only for vetted US organisations; API ID claude-mythos-5-1. Retirement not sooner than September 1, 2027; this is a minimum commitment, not an announced shutdown.

BudgetRecord checked October 1, 2026

Claude Haiku 4.5

Claude Haiku 4.5 is Anthropic's lower-cost Haiku tier for high-volume classification and extraction at $1/$5 per million input/output tokens.

Best for

High-volume classification
Routine extraction
Latency-sensitive stacks

Watch out

No adaptive thinking (manual extended thinking via budget_tokens only); 200K context. Anthropic lists 2026-10-15 as the earliest possible retirement date, and Haiku 5.5 is announced but not released.

FrontierRecord checked October 1, 2026

Claude Mythos 5.1

Anthropic describes Claude Mythos 5.1 as its 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 for vetted US organisations through trusted access programmes, with 30-day retention required by default for safety monitoring. Adaptive thinking cannot be disabled and forced tool use errors. Shared underlying model does not make Fable benchmark results Mythos observations; safeguards and access differ.

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. This compares standard short-context token rates, not total cost per accepted task. Include input, cache, context tiers, schedules, retries and review in your pilot.

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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.
4/5 core specs verified on both sides — Not published for at least one side: parameter count.
No directly aligned benchmark setup — No benchmark has matching cited sources, source dates, units, effort and recorded run details on both models.
Verified within the last 90 days — Older of the two catalog checks was 25 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: Claude model overview — whole-profile source check October 1 (accessed 2026-10-01)
Claude Haiku 4.5: Claude current API pricing, caching and inference geography (accessed 2026-10-01)
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: Claude model overview — whole-profile source check October 1 (accessed 2026-10-01)
Claude Mythos 5.1: Claude current API pricing, caching and inference geography (accessed 2026-10-01)
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)
Claude Mythos 5.1: Anthropic — Mythos 5.1 overview (1M context, 128K output, claude-mythos-5-1) (accessed 2026-09-26)
Claude Mythos 5.1: Anthropic selectable effort levels (separate from adaptive thinking mode) (accessed 2026-10-01)

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. Estimate both input and output token volume for your workload. These are base rates; Claude Haiku 4.5: Standard $1/$5 per MTok; cache reads $0.10, 5-minute writes $1.25 and 1-hour writes $2. Batch $0.50/$2.50. Context 200K and output 64K. Reliable knowledge cutoff Feb 2025; training cutoff Jul 2025. The alias claude-haiku-4-5 resolves to claude-haiku-4-5-20251001. Retirement not sooner than October 15, 2026; no definite shutdown is announced. Claude Mythos 5.1: Standard $10/$50 per MTok, sharing Fable 5.1's specifications/pricing. Cache reads $0.25; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Invite-only for vetted US organisations; API ID claude-mythos-5-1. Retirement not sooner than September 1, 2027; this is a minimum commitment, not an announced shutdown.

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. Estimate both input and output token volume for your workload. These are base rates; Claude Haiku 4.5: Standard $1/$5 per MTok; cache reads $0.10, 5-minute writes $1.25 and 1-hour writes $2. Batch $0.50/$2.50. Context 200K and output 64K. Reliable knowledge cutoff Feb 2025; training cutoff Jul 2025. The alias claude-haiku-4-5 resolves to claude-haiku-4-5-20251001. Retirement not sooner than October 15, 2026; no definite shutdown is announced. Claude Mythos 5.1: Standard $10/$50 per MTok, sharing Fable 5.1's specifications/pricing. Cache reads $0.25; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Invite-only for vetted US organisations; API ID claude-mythos-5-1. Retirement not sooner than September 1, 2027; this is a minimum commitment, not an announced shutdown.

Which has the larger context window, Claude Haiku 4.5 or Claude Mythos 5.1?

Claude Mythos 5.1 accepts 1M tokens against 200K for Claude Haiku 4.5. This only matters if you routinely send very long documents or large codebases.

Do Claude Haiku 4.5 and Claude Mythos 5.1 support the same reasoning levels?

Claude Haiku 4.5 exposes extended thinking (budget_tokens), while Claude Mythos 5.1 exposes low, medium, high, xhigh, max.

Should I use Claude Haiku 4.5 or Claude Mythos 5.1?

We classify Claude Haiku 4.5 in the budget tier and Claude Mythos 5.1 in the frontier tier. Test whether either meets your accuracy, tool-use and latency requirements before choosing on price.

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.
Context: Claude Mythos 5.1 takes 1M against 200K for Claude Haiku 4.5 — only decisive if your prompts approach the smaller window.
Positioning: Claude Haiku 4.5 sits in the budget tier, Claude Mythos 5.1 in the frontier tier. Compare accuracy, reliability, latency, and cost on representative tasks before choosing.

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