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Model comparison

Claude Mythos 5.1 vs GLM 5.3

Anthropic against Z.ai, compared on context, price, and attributed benchmark results.

Recorded profile verification October 2, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Mythos 5.1

Frontier

vs

Z.ai

GLM 5.3

Frontier · Open weights

AI model capability comparison
SpecificationClaude Mythos 5.1GLM 5.3
ProviderAnthropicZ.ai
TierFrontierFrontier
Context window1M1M
Max output128KWinner: 131K
Input / 1M tokens$10Winner: $1.40
Output / 1M tokens$50Winner: $4.40
WeightsClosedOpen
ParametersNot verifiedUnverified753B total (MoE; active count not verified)
Reasoning levelslow, medium, high, xhigh, maxlow, high, max
Modalitiestext, imagetext
LicenseNot verifiedUnverifiedGLM-5.3 License (custom)
API model idclaude-mythos-5-1glm-5.3
ReleasedSeptember 1, 2026August 14, 2026
Artificial Analysis Intelligence Index [max] · source date GLM 5.3: 2026-10-01Not verifiedUnverified45
Terminal-Bench 2.1 · source date GLM 5.3: 2026-08-14Not verifiedUnverified88.2
DeepSWE 1.1 · source date GLM 5.3: 2026-08-14Not verifiedUnverified66.9
Humanity's Last Exam · source date GLM 5.3: 2026-08-14Not verifiedUnverified62.5

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 date2026-10-01
    Artificial Analysis (GLM-5.3 (max))

    Composite index blending reasoning, knowledge, and coding evals into one 0–100 score.

    Comparable with caveatOnly same-version scores are comparable. v4.3.2 was rebaselined (the top score fell from 66 on v4.1.1 to ~58), so v4.1.1 figures must not be compared with v4.3.2 figures — check the cited source and its date.

  • Source date2026-08-14
    Z.ai GLM-5.3 blog + HF model card (vendor, with tools, full set)

    Frontier-knowledge ceiling: extremely hard multi-domain questions written to be near-impossible without deep expertise.

    Comparable with caveatSubset/tool configurations (text-only vs with-tools) differ between vendors and materially change scores; must match configuration to compare.

  • Source date2026-08-14
    Z.ai GLM-5.3 blog + HF model card (vendor, mini-swe-agent family)

    Agentic software engineering: pass@1 on real repo tasks with reported cost per completed task.

    Directly comparable

  • Source date2026-08-14
    Z.ai GLM-5.3 blog + HF model card eval results (vendor, Claude Code harness)

    Agentic terminal work: multi-step tasks executed in a sandboxed shell environment.

    Comparable with caveatNot comparable with Terminal-Bench 3.0 or 4.0 (different task sets) or v1; harness configuration (container, time limits) also shifts results.

Pricing tiers

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.

GLM 5.3: Z.ai token API $1.40/$4.40 per MTok; cached input $0.26. Cache storage is listed as limited-time free, with no verified end date. Coding Plan points are separate: off-peak/weekend calls consume half the standard points. API docs advertise 1M context and specify a 131,072 output ceiling.

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.

FrontierOpen weightsRecord checked October 2, 2026

GLM 5.3

Z.ai's text-only GLM flagship, with a 753B-total MoE checkpoint and always-enabled reasoning. Published benchmark figures identify particular harnesses and settings.

Best for

  • Coding Plan subscribers
  • Long-horizon coding
  • Chinese + English

Watch out

Custom licence: model-as-a-service operators whose licensee/affiliate aggregate revenue exceeds $10B in any consecutive 12 months require Z.AI security review before commercial use; the definition excludes embedded end-user features/harnesses and mere relays. Keep attribution/permission notices. Reasoning defaults to max; disabling it fails. Accounts that ever subscribed to Coding Plan, including expired subscriptions, currently have Model API access only through the Chat Completions-compatible protocol. Active parameter count and exact initial weight-publication day remain unverified.

When the cheaper one wins

GLM 5.3 is cheaper on output at $4.40 per million tokens against $50 for Claude Mythos 5.1 — about 11×. 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.

Run the model picker

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.

Related comparisons

Diving deeper on one model? Claude Mythos 5.1 · GLM 5.3

Common questions

Claude Mythos 5.1 vs GLM 5.3

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

Is Claude Mythos 5.1 or GLM 5.3 cheaper for input?
GLM 5.3 is cheaper at $1.40 per million input tokens, against $10 for Claude Mythos 5.1 — roughly 7.1× the price. Estimate both input and output token volume for your workload. These are base rates; 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. GLM 5.3: Z.ai token API $1.40/$4.40 per MTok; cached input $0.26. Cache storage is listed as limited-time free, with no verified end date. Coding Plan points are separate: off-peak/weekend calls consume half the standard points. API docs advertise 1M context and specify a 131,072 output ceiling.
Is Claude Mythos 5.1 or GLM 5.3 cheaper for output?
GLM 5.3 is cheaper at $4.40 per million output tokens, against $50 for Claude Mythos 5.1 — roughly 11× the price. Estimate both input and output token volume for your workload. These are base rates; 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. GLM 5.3: Z.ai token API $1.40/$4.40 per MTok; cached input $0.26. Cache storage is listed as limited-time free, with no verified end date. Coding Plan points are separate: off-peak/weekend calls consume half the standard points. API docs advertise 1M context and specify a 131,072 output ceiling.
Which has the larger context window, Claude Mythos 5.1 or GLM 5.3?
Both accept about 1M tokens of context, so document length will not decide between them.
Do Claude Mythos 5.1 and GLM 5.3 support the same reasoning levels?
Claude Mythos 5.1 exposes low, medium, high, xhigh, max, while GLM 5.3 exposes low, high, max.
Should I use Claude Mythos 5.1 or GLM 5.3?
Both are classified in our frontier tier; this editorial grouping does not imply equal capability. Claude Mythos 5.1 is a candidate for cyber-defence research; GLM 5.3 is a candidate for coding plan subscribers. Compare accuracy, tool reliability, latency and cost on representative tasks.
Can I self-host Claude Mythos 5.1 or GLM 5.3?
GLM 5.3 publishes open weights, but self-hosting and third-party provider access depend on the licence, hardware, serving support, and availability. Claude Mythos 5.1 is a closed model whose supported access paths are controlled by its provider.

Next step

Choosing between them

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

  • Input price: GLM 5.3 costs $1.40 per 1M tokens versus $10 for Claude Mythos 5.1 — a 7.1x difference at the headline tier.
  • Deployment: GLM 5.3 publishes weights you can self-host; the other is API-only.
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