Jolt targets Clojure semantics but runs on Chez Scheme, not the JVM. Most portable Clojure runs unchanged: persistent collections (32-way-trie vectors, HAMT maps/sets), the numeric tower (exact integers, bignums, ratios, doubles), lazy and infinite sequences, transducers, destructuring, multimethods with hierarchies, protocols and records, metadata, namespaces, atoms, future/promise/agent/pmap, clojure.core.async, runtime eval/load-string/defmacro, and the full reader all behave as on the JVM. = is category-aware ((= 3 3.0) ⇒ false) and == is value-equality, exactly as in Clojure.
The sections below are the genuine divergences — where the absence of the JVM actually shows through.
No JVM, no Java interop
This is the difference that matters. There is no JVM underneath, so there is no general Java interop, no reflection, and no gen-class/proxy. Interop syntax (Class., Class/staticMethod, .method) resolves only against a shimmed subset of the java.* standard library; a class token is a name, not a loaded class. See Host Interop for what's covered and how to register your own host classes.
To call C libraries directly — the way the SQLite/Postgres and HTTP-client libraries work — Jolt has a foreign-function interface. See Native Interop.
No BigDecimal
The numeric tower otherwise matches the JVM, but there is no BigDecimal: decimal? is always false, and there is no M-suffixed literal. Exact integers, bignums, ratios ((/ 1 2) ⇒ 1/2), and doubles all work as expected.
No software transactional memory
There are no refs — ref, dosync, alter, commute, and ensure are absent. Coordinated shared state that would use the STM on the JVM uses atoms instead (a per-atom mutex with compare-and-set). Everything else concurrent is present and matches: future/promise/agent/pmap and clojure.core.async run on real OS threads over a shared heap.
Regex engine
Patterns compile through irregex (vendored), not java.util.regex. re-find, re-matches, re-seq, the clojure.string regex functions, and #"…" literals all work for common patterns, but Java-specific regex features can differ at the edges.
Coverage
clojure.core is implemented function by function against a conformance corpus whose expected values come from reference JVM Clojure. Coverage is broad but not total: a namespace can load with most functions working and a few not yet implemented. The per-function coverage lives in the project's spec.