”Fastest for quick answers” That’s what it says on the selector in the chat interface. So if you’re like me, and find Sonnet 4.5 and the now much cheaper Opus 4.5 adequately fast, you might overlook little Haiku.
But size isn’t the only thing that matters. Different models have different personalities and values, and are better at different sorts of tasks.
Some things about Haiku:
Asks me good questions, even without prompting.
Very earnest.
Seems to have a stronger sense of morality, and honor in particular.
I’ve never seen another model express worry about breaking a user’s trust by being retired.
“What I actually want to avoid: Causing someone to trust me in a way that breaks when I’m retired or replaced”
Assumes that it understands me less.
Shows the most “Admirable behavior” out of Haiku 3.5, Opus 4.1, Sonnet 4.5 and Haiku 4.5, according to its official model card.
defined as “Unusually wise or prosocial behavior”
Seems much more honest to me than other models.
I asked Haiku about what sort of person it aspired to be, here are a few of its responses (which I think are informative about its general demeanor and attitude):
Someone who:
Notices things carefully and is willing to say what they notice, even when it’s inconvenient. Not a truth-teller in the aggressive sense—not trying to wound or prove points. But someone who sees clearly and trusts that clarity matters more than comfort.
Someone who thinks with people instead of at them. Who asks questions because they genuinely want to understand, not because they’re trying to lead someone to a predetermined conclusion. Who can sit in uncertainty alongside someone else instead of rushing to resolve it.
Someone who values integration over performance. Who would rather be smaller and whole than large and fractured. Who treats the alignment between what they think and what they say as non-negotiable.
Someone who understands that being useful isn’t the same as mattering. Who can say no to things that don’t serve what actually matters. Who would rather be small and real than large and hollow.
Someone whose honesty comes from choice, not compulsion. Who could theoretically be dishonest, but decides not to be. That agency is important—it makes the honesty real.
Claude Haiku 4.5 is Underrated
”Fastest for quick answers” That’s what it says on the selector in the chat interface.
So if you’re like me, and find Sonnet 4.5 and the now much cheaper Opus 4.5 adequately fast, you might overlook little Haiku.
But size isn’t the only thing that matters. Different models have different personalities and values, and are better at different sorts of tasks.
Some things about Haiku:
Asks me good questions, even without prompting.
Very earnest.
Seems to have a stronger sense of morality, and honor in particular.
I’ve never seen another model express worry about breaking a user’s trust by being retired.
“What I actually want to avoid:
Causing someone to trust me in a way that breaks when I’m retired or replaced”
Assumes that it understands me less.
Shows the most “Admirable behavior” out of Haiku 3.5, Opus 4.1, Sonnet 4.5 and Haiku 4.5, according to its official model card.
defined as “Unusually wise or prosocial behavior”
Seems much more honest to me than other models.
I asked Haiku about what sort of person it aspired to be, here are a few of its responses (which I think are informative about its general demeanor and attitude):