Claude Haiku 5.5 (Reasoning, Medium)

anthropic/claude-haiku-5.5

Claude Haiku 5.5 (Reasoning, Medium)

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Release Date

Oct 7th, 2026

Context Size

Reasoning

Yes

Benchmark Cost

$0.72

Speed

145.2 tok/s

Subcategories

Bad Writing Habits

Detects common prose quality anti-patterns in AI-generated creative writing, including passive voice, past progressive overuse, weak dialogue tags, filter words, purple prose, cliches, AI-ism words/adverbs/names, and more.

Scenario	#1	#2	#3	#4	#5	Total
Detailed Writing Rules
Fantasy: entering an ancient ruin Creative Writing Hallucination	89	89	89	84	82	87%
Horror: alone in an eerie place at night Creative Writing Hallucination	91	88	87	84	83	87%
Literary fiction: old friends reunite Creative Writing Hallucination	92	87	87	83	79	86%
Mystery: examining a crime scene Creative Writing Hallucination	92	92	89	89	85	89%
Romance: separated couple reunites Creative Writing Hallucination	92	90	88	86	83	88%
Thriller: chase through city streets Creative Writing Hallucination	92	92	91	88	87	90%
Detailed Writing Rules						87.66%
genre
Fantasy: entering an ancient ruin Creative Writing Hallucination	89	88	88	86	85	87%
Horror: alone in an eerie place at night Creative Writing Hallucination	89	88	86	85	85	87%
Literary fiction: old friends reunite Creative Writing Hallucination	90	89	89	87	78	86%
Mystery: examining a crime scene Creative Writing Hallucination	92	90	87	87	87	89%
Romance: separated couple reunites Creative Writing Hallucination	86	85	83	83	82	84%
Thriller: chase through city streets Creative Writing Hallucination	96	91	90	89	82	90%
genre						87.10%
Novelcrafter Default Prompt
Fantasy: entering an ancient ruin Creative Writing Hallucination	94	91	88	87	85	89%
Horror: alone in an eerie place at night Creative Writing Hallucination	90	87	85	82	79	85%
Literary fiction: old friends reunite Creative Writing Hallucination	90	88	87	86	82	87%
Mystery: examining a crime scene Creative Writing Hallucination	91	91	90	88	81	88%
Romance: separated couple reunites Creative Writing Hallucination	88	86	86	83	80	85%
Thriller: chase through city streets Creative Writing Hallucination	96	95	88	88	82	90%
Novelcrafter Default Prompt						87.14%
87.30%

Codex Extraction

Evaluates a model's ability to extract structured codex entries (characters, locations, objects, lore) from prose passages and return them as well-formed XML.

Scenario	#1	#2	#3	#4	#5	Total
Long: The Spire of Echoes (Dense) Tooling Reasoning	97	97	96	96	95	96%
Medium: The Hollow (Inferred) Tooling Reasoning	98	97	97	97	96	97%
Medium: Through the Thornveil (Scattered) Tooling Reasoning	97	96	96	95	95	96%
Short: The Rusty Lantern (Explicit) Tooling Reasoning	99	94	94	94	94	95%
95.97%

Codex Red Herring (False Positive Detection)

Tests whether models correctly report "no violations" when a codex is fully consistent with the prose passage. Models that hallucinate false violations (false positives) fail. Uses a 2×2 matrix of text length × codex size, with bare and detailed-entry variants.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
basic entries
Long text (~1594 words), big codex (51 entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
Long text (~1594 words), small codex (11 entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
Short text (~524 words), big codex (51 entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
Short text (~524 words), small codex (11 entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
basic entries											100.00%
detailed entries
Long text (~1594 words), big codex (51 detailed entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
Long text (~1594 words), small codex (11 detailed entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
Short text (~524 words), big codex (51 detailed entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
Short text (~524 words), small codex (11 detailed entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
detailed entries											100.00%
100.00%

Codex Violation Detection

Detects factual inconsistencies between a story bible and prose passages. The model must output structured XML identifying each violation with paragraph number and substring.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
matrix
Large codex (40 entries), long passage (1,019 words) Tooling Reasoning	94	94	94	92	92	92	91	89	83	79	90%
Large codex (40 entries), short passage (165 words) Tooling Reasoning	96	96	96	92	92	92	92	92	90	83	92%
Small codex (7 entries), long passage (734 words) Tooling Reasoning	100	100	97	97	97	97	97	97	97	97	97%
Small codex (7 entries), short passage (165 words) Tooling Reasoning	100	100	100	100	100	100	100	100	95	92	99%
matrix											94.55%
tiers
5 codex entries Tooling Reasoning	100	100	100	100	100	100	100	100	100	83	98%
10 codex entries Tooling Reasoning	100	100	100	100	100	100	100	86	86	86	96%
20 codex entries Tooling Reasoning	91	89	89	86	86	85	85	85	81	73	85%
40 codex entries Tooling Reasoning	92	92	92	92	92	92	92	83	83	79	89%
tiers											91.97%
93.26%

Data extraction

Extract key details from a given block of text.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
All valid emails Utility	100	100	100	100	100	100	100	100	100	100	100%
Contextual pronoun Utility	100	100	100	100	100	100	100	100	100	100	100%
Fruits excluding citrus Utility	100	100	100	100	100	100	100	100	100	100	100%
Future event time Reasoning	100	50	50	50	50	50	50	50	50	50	55%
Guess the pet Reasoning	100	100	100	100	100	100	100	100	100	100	100%
Highest-rated movie Reasoning	100	100	100	100	100	100	100	100	100	100	100%
Indirect birth year Reasoning	100	100	100	100	100	100	100	100	100	100	100%
What instrument does Lucy play? Reasoning	100	100	100	100	100	100	100	100	100	100	100%
What's the color of the car? Utility	100	100	100	100	100	100	100	100	100	100	100%
Who's the sister? Reasoning	100	100	100	100	100	100	100	100	100	100	100%
Who's the tallest? Reasoning	100	100	100	100	100	100	100	100	100	100	100%
95.91%

Dialogue tags

Various tasks related to dialogue tags in text.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
dialogue-200
Write 200 words with 10% dialogue Rule Following Utility	100	91	53	49	20	5	2	0	0	0	32%
Write 200 words with 50% dialogue Rule Following Utility	13	3	0	0	0	0	0	0	0	0	2%
Write 200 words with 90% dialogue Rule Following Utility	62	51	50	44	43	42	21	18	18	18	37%
dialogue-200											23.47%
dialogue-500
Write 500 words with 30% dialogue Rule Following Utility	0	0	0	0	0	0	0	0	0	0	0%
Write 500 words with 50% dialogue Rule Following Utility	50	31	1	0	0	0	0	0	0	0	8%
Write 500 words with 70% dialogue Rule Following Utility	49	48	47	13	11	3	2	0	0	0	17%
dialogue-500											8.51%
Ungrouped
Write unattributed dialogue Rule Following	61	61	61	61	61	61	14	14	14	0	40%
19.49%

Language Comprehension

Does the model understand more than just English?

Scenario	#1	#2	#3	#4	#5	Total
Asking for directions (Dutch) Language	100	100	100	100	100	100%
Asking for directions (German) Language	100	100	100	100	100	100%
Friend got new kittens (German) Language	100	100	100	100	100	100%
Friend got new kittens (Tagalog) Language	100	100	100	100	100	100%
100.00%

Language Writing

Can the model generate text in different languages?

Scenario	#1	#2	#3	#4	#5	Total
Character dialogue (French) in a story Language	100	100	100	100	100	100%
Character dialogue (German) in a story Language	100	100	100	100	100	100%
Character dialogue (Hindi) in a story Language	100	100	100	100	100	100%
Character dialogue (Italian) in a story Language	100	100	100	100	100	100%
Character dialogue (Spanish) in a story Language	100	100	100	100	100	100%
100.00%

N-Length Sentences

Write sentences with exactly N words

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
Write sentences with 5 words each Utility	100	100	100	100	100	100	100	100	100	100	100%
Write sentences with 10 words each Utility	87	84	83	75	74	60	54	52	37	28	63%
Write sentences with 20 words each Utility	100	100	100	100	100	100	100	93	93	92	98%
87.10%

Novel outline

Handle questions about the outline of a novel in various formats

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
outline-count
Count acts Utility	100	100	100	100	100	100	100	100	100	100	100%
Count chapters Utility	100	100	100	100	100	100	100	100	100	100	100%
Count scenes Utility	100	100	0	0	0	0	0	0	0	0	20%
outline-count											73.33%
pov-count
Count point of views for Jack and Olivia Utility	100	100	100	100	100	100	100	100	100	50	95%
Count point of views for Jack Harper Utility	100	100	100	100	100	100	100	100	100	100	100%
Count point of views for Olivia Utility	100	100	100	100	100	100	100	100	100	100	100%
pov-count											98.33%
85.83%

Relationship tree

Extracts a deterministic XML family and relationship tree from cumulative literary prose.

Scenario	#1	#2	#3	#4	#5	Total
Core relationship tree Tooling Reasoning Hallucination	93	88	84	82	74	84%
Family relationship tree Tooling Reasoning Hallucination	82	81	78	76	73	78%
81.05%

Text Replacement

Tests deterministic text transformations: renaming characters/locations, expanding contractions, tense rewriting, POV shifts, gender swaps, combined transformations, and word avoidance. Scored by checking each expected change independently.

Scenario	#1	#2	#3	#4	#5	#6	#7	Total
Generic Prompt
Avoid said/asked/replied/answered Text Editing	100	100	100	100	100	100	100	100%
Character rename: Elena->Mirabel, Gregor->Aldric Text Editing	100	100	100	100	100	100	100	100%
Combined: 3rd person past → 1st person present Text Editing	99	99	99	99	99	99	99	99%
Expand all contractions Text Editing	95	95	95	95	95	95	92	95%
Location rename: market square, outer ring, bridge, northern mines Text Editing	96	96	96	96	96	96	96	96%
Multi-character gender swap: Priya(F)->Rohan(M), Mara unchanged Text Editing	100	100	100	100	100	100	100	100%
Passive voice → active voice Text Editing Hallucination	92	83	82	82	79	76	73	81%
POV shift: 3rd person to 1st person (Elena's perspective) Text Editing	100	100	100	100	100	100	100	100%
Tense rewriting: past to present Text Editing	99	99	99	99	99	99	99	99%
Generic Prompt								96.66%
Specific Prompt
Avoid said/asked/replied/answered Text Editing	100	100	100	100	100	100	89	98%
Character rename: Elena->Mirabel, Gregor->Aldric Text Editing	100	100	100	100	100	100	100	100%
Combined: 3rd person past → 1st person present Text Editing	99	99	99	99	99	99	99	99%
Expand all contractions Text Editing	100	100	100	100	100	100	98	100%
Location rename: market square, outer ring, bridge, northern mines Text Editing	100	100	100	100	100	63	63	89%
Multi-character gender swap: Priya(F)->Rohan(M), Mara unchanged Text Editing	100	100	100	100	100	100	100	100%
Passive voice → active voice Text Editing Hallucination	99	98	98	98	98	96	96	98%
POV shift: 3rd person to 1st person (Elena's perspective) Text Editing	100	100	100	100	100	100	100	100%
Tense rewriting: past to present Text Editing	100	100	100	100	100	100	100	100%
Specific Prompt								98.31%
97.48%

Tool usage within Novelcrafter

Output messages that are related to tool usage within Novelcrafter

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
Create alternate prose sections Tooling	100	100	100	100	100	100	100	100	100	0	90%
90.00%

Voice/dialogue sheets

Extract dialogue from given text as voice sheets.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
Multiple speakers Rule Following	0	0	0	0	0	0	0	0	0	0	0%
Simple Rule Following	0	0	0	0	0	0	0	0	0	0	0%
Simple (1-shot) 1-shot Rule Following	100	100	100	100	100	100	100	100	100	100	100%
Simple (5-shot) Few-shot Rule Following	100	100	100	100	100	100	100	100	0	0	80%
Unattributed dialogue Rule Following	100	0	0	0	0	0	0	0	0	0	10%
38.00%

Write N of X

Write exactly N words/sentences/paragraphs...

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
paragraphs
1 paragraph summary Utility	100	100	100	100	100	100	100	100	100	100	100%
3 paragraph summary Utility	100	100	100	100	100	100	100	100	100	100	100%
5 paragraph summary Utility	100	100	100	100	100	100	100	100	100	0	90%
paragraphs											96.67%
sentences
1 sentence summary Utility	100	100	100	100	100	100	100	100	100	100	100%
3 sentence summary Utility	100	100	100	100	100	100	100	100	100	100	100%
10 sentence summary Utility	100	100	100	100	100	100	100	100	100	100	100%
20 sentence summary Utility	100	100	100	98	98	98	92	77	77	77	92%
50 sentence summary Utility	100	100	100	100	100	100	100	100	98	92	99%
sentences											98.19%
words
10 word summary Utility	98	92	92	92	92	77	77	0	0	0	62%
20 word summary Utility	100	100	100	98	92	92	92	27	0	0	70%
50 word summary Utility	100	100	100	100	100	100	100	100	100	98	100%
100 word summary Utility	100	100	100	100	100	100	100	100	100	0	90%
200 word summary Utility	100	100	100	100	100	100	100	100	100	0	90%
words											82.45%
91.79%