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AI Choice Engine

Model comparison

Claude Haiku 5.5 vs Claude Mythos 5.1

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

Claude Haiku 5.5: profile checked October 25, 2026Claude Mythos 5.1: profile checked October 25, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Haiku 5.5

Budget

vs

Anthropic

Claude Mythos 5.1

Frontier

AI model capability comparison
SpecificationClaude Haiku 5.5Claude Mythos 5.1
ProviderAnthropicAnthropic
TierBudgetFrontier
Context window1M1M
Max output128K128K
Input / 1M tokensWinner: $0.10$10
Output / 1M tokensWinner: $0.50$50
WeightsNot verifiedUnverifiedClosed
ParametersNot verifiedUnverifiedNot verifiedUnverified
Reasoning levelsNot verifiedUnverifiedlow, medium, high, xhigh, max
Modalitiestext, imagetext, image
API model idclaude-haiku-5-5claude-mythos-5-1
ReleasedOctober 7, 2026September 1, 2026

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.

Pricing tiers

Claude Haiku 5.5: Base rates apply to prompts up to 100,000 tokens. Above 100,000 tokens, input is $0.50 and output $2.50 per MTok. Cache reads are $0.01/$0.05; 5-minute writes $0.125/$0.625 and 1-hour writes $0.20/$1 for short/long prompts. Batch input/output receives a 50% discount. Standard output is 128K; 300K Batch output requires the documented beta header. Adaptive thinking defaults to medium effort.

Claude Mythos 5.1: Standard USD/MTok input/output $10/$50, matching Fable 5.1; cache reads $0.25, 5-minute writes $12.50, 1-hour writes $20. Batch $5/$25. US-only inference adds 10% to input/output and cache reads/writes on Anthropic-operated routes where supported; Foundry uses US Data Zone Standard. Bedrock and Google-managed Google Cloud have independent regional prices. Access requires verification; the public API ID does not grant entitlement. Retirement not sooner than September 1, 2027 is a minimum commitment, not an announced shutdown. Server-side tools can add usage fees; tool schemas/results and thinking consume billable tokens.

BudgetRecord checked October 25, 2026

Claude Haiku 5.5

Anthropic positions Haiku 5.5 for high-volume classification, extraction, routing and subagent tasks, with adaptive thinking and a 1M-token context window.

Best for

  • Classification and extraction
  • Routing
  • High-volume subagent tasks

Watch out

Prices increase fivefold above 100K prompt tokens. The newer tokenizer counts approximately 30% more tokens than Haiku 4.5 for the same text. Omit temperature, top_p and top_k. Thinking blocks are reusable only in the producing account or a linked account. Parameter count and weight availability remain unverified; no predecessor benchmark scores are inherited.

FrontierRecord checked October 25, 2026

Claude Mythos 5.1

Claude Fable 5.1's underlying capabilities for organisations verified for cybersecurity or life-sciences research, with different cyber/bio safeguards and access controls.

Best for

  • Cyber-defence research
  • Biology research
  • Claude Security workloads

Watch out

Access requires an applicable verification programme; current primary sources do not establish a universal country eligibility list. Accepting 30-day data retention for safety monitoring is required by default. Adaptive thinking is always on and forced tool use errors. Shared underlying capabilities do not make Fable benchmark results Mythos observations; safeguards, fallback behavior and evaluation setups differ.

When the cheaper one wins

Claude Haiku 5.5 is cheaper on output at $0.50 per million tokens against $50 for Claude Mythos 5.1 — about 100×. 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.
  • 3/5 core specs verified on both sides — Not published for at least one side: parameter count, reasoning levels.
  • 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 1 day ago.
  • Source citations incomplete — At least one side lacks the two-source citation set.

Source receipts

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

Related comparisons

Diving deeper on one model? Claude Haiku 5.5 · Claude Mythos 5.1

Common questions

Claude Haiku 5.5 vs Claude Mythos 5.1

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

Is Claude Haiku 5.5 or Claude Mythos 5.1 cheaper for input?
Claude Haiku 5.5 is cheaper at $0.10 per million input tokens, against $10 for Claude Mythos 5.1 — roughly 100× the price. Estimate both input and output token volume for your workload. These are base rates; Claude Haiku 5.5: Base rates apply to prompts up to 100,000 tokens. Above 100,000 tokens, input is $0.50 and output $2.50 per MTok. Cache reads are $0.01/$0.05; 5-minute writes $0.125/$0.625 and 1-hour writes $0.20/$1 for short/long prompts. Batch input/output receives a 50% discount. Standard output is 128K; 300K Batch output requires the documented beta header. Adaptive thinking defaults to medium effort. Claude Mythos 5.1: Standard USD/MTok input/output $10/$50, matching Fable 5.1; cache reads $0.25, 5-minute writes $12.50, 1-hour writes $20. Batch $5/$25. US-only inference adds 10% to input/output and cache reads/writes on Anthropic-operated routes where supported; Foundry uses US Data Zone Standard. Bedrock and Google-managed Google Cloud have independent regional prices. Access requires verification; the public API ID does not grant entitlement. Retirement not sooner than September 1, 2027 is a minimum commitment, not an announced shutdown. Server-side tools can add usage fees; tool schemas/results and thinking consume billable tokens.
Is Claude Haiku 5.5 or Claude Mythos 5.1 cheaper for output?
Claude Haiku 5.5 is cheaper at $0.50 per million output tokens, against $50 for Claude Mythos 5.1 — roughly 100× the price. Estimate both input and output token volume for your workload. These are base rates; Claude Haiku 5.5: Base rates apply to prompts up to 100,000 tokens. Above 100,000 tokens, input is $0.50 and output $2.50 per MTok. Cache reads are $0.01/$0.05; 5-minute writes $0.125/$0.625 and 1-hour writes $0.20/$1 for short/long prompts. Batch input/output receives a 50% discount. Standard output is 128K; 300K Batch output requires the documented beta header. Adaptive thinking defaults to medium effort. Claude Mythos 5.1: Standard USD/MTok input/output $10/$50, matching Fable 5.1; cache reads $0.25, 5-minute writes $12.50, 1-hour writes $20. Batch $5/$25. US-only inference adds 10% to input/output and cache reads/writes on Anthropic-operated routes where supported; Foundry uses US Data Zone Standard. Bedrock and Google-managed Google Cloud have independent regional prices. Access requires verification; the public API ID does not grant entitlement. Retirement not sooner than September 1, 2027 is a minimum commitment, not an announced shutdown. Server-side tools can add usage fees; tool schemas/results and thinking consume billable tokens.
Which has the larger context window, Claude Haiku 5.5 or Claude Mythos 5.1?
Both accept about 1M tokens of context, so document length will not decide between them.
Should I use Claude Haiku 5.5 or Claude Mythos 5.1?
We classify Claude Haiku 5.5 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 5.5 costs $0.10 per 1M tokens versus $10 for Claude Mythos 5.1 — a 100x difference at the headline tier.
  • Positioning: Claude Haiku 5.5 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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