yminsky

$ opam install async_extra.112.24.00 --dry-run
The following actions will be performed:
 - remove    core_bench.112.17.00
 - upgrade   pa_ounit from 112.17.00 to 112.24.00  [required by async_extra]
 - downgrade zarith from 1.3 to 1.2                [required by asn1-combinators]
 - upgrade   bin_prot from 112.17.00 to 112.24.00  [required by async_extra]
 - upgrade   sexplib from 112.17.00 to 112.24.00   [required by async_extra]
 - recompile pa_bench.112.06.00                    [uses pa_ounit]
 - recompile uri.1.8.0                             [uses sexplib]
 - upgrade   typerep from 112.17.00 to 112.24.00   [uses bin_prot]

yminsky

$ opam upgrade -v
Everything as up-to-date as possible.
The following newer versions couldn't be installed:
  - base-bytes.legacy is not available because it requires OCaml < 4.02.0.
  - camlp4.4.03.0 is not available because it requires OCaml >= 4.03.0.
The following would require downgrades or uninstalls, but you may upgrade them explicitely:
  - async.112.24.00
  - async_extra.112.24.00
  - async_kernel.112.24.00
  - async_unix.112.24.00